When constructing an airplane fuselage, the fuselage is often assembled longitudinally from generally cylindrical sections of fuselage. These individual cylindrical fuselage sections are constructed from panels. For example, a fuselage section of a BOEING 777 is formed from four panels: a keel panel at the bottom, opposing side panels on either side, and a crown panel on top. As will be understood, when assembling these panels into a fuselage section, the circumference of the fuselage is very important. If a fuselage section is constructed with an incorrect circumference, it will not mate properly with adjacent sections.
Prior art assembly techniques for maintaining consistency of fuselage section circumference involved the use of a Floor Assembly Jig (FAJ). The FAJ was essentially a form around which the fuselage panels could be assembled, thereby ensuring correct circumferences. However, new assembly techniques have made the use of a FAJ obsolete. With the introduction of Fuselage Automated Upright Build (FAUB) techniques and devices for the 777, the fuselage is built without the use of a FAJ to help maintain circumference consistency.
Laser radars have been used to measure the circumference of an assembled fuselage section. However, this technique has several drawbacks. The setup time for the laser radar is approximately 4 hours. Additionally, the laser radar itself is heavy—generally more than 100 pounds—and its overall size reduces mobility. Additionally, the actual measurement period lasts thirty minutes or more. Thus, existing techniques are unwieldy and inefficient.
In addition, when constructing a fuselage section from various panels, or when constructing the fuselage from various fuselage sections, measurements other than circumference are important. For example, the longitudinal lap splice (i.e., gaps between the laps of each of the four panels along the length of a fuselage section) and circumferential splice areas (i.e., circumferential gaps between fuselage sections) are the integration zones between skin panels. These areas have strict engineering requirements that are important to the fatigue life of the airplane.
In the past, techniques for monitoring splice centered around manual validation. A worker would insert a tapered gauge into each gap at every frame bay and around the entire circumference of the fuselage. This technique is time consuming and difficult, considering the fuselage is constructed high above the ground with the introduction of FAUB. Indeed, the existing manual techniques require lengthy scaffolding moves to capture data high above the ground. Thus, existing validation techniques are undesirable for current FAUB construction methodologies.